To provide theoretical basis for the production of pellets, the effect of BaSO4 in the range of 0 to 5.0% on properties of pellets was studied under experimental conditions. The influence mechanism of BaSO4 on the compressive strength of preheated pellets as well as roasted pellets and reduction behavior of roasted pellets was investigated by means of scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). From the results, it can be observed that the compressive strength of preheated pellets varies slightly whereas roasted pellets has a great change when BaSO4 content increases from 0 to 5%. The compressive strength of roasted pellets initially increases then decreases, which reaches the peak value of 3411 N with BaSO4 content of 1.5%. The reduction degree enhances from 80.7 to 97.9% and FeO content reduces from 2.33 to 1.57% with increasing BaSO4 content from 0 to 5.0%. The degree of polycrystalline of hematite improves and the hole size increases obviously when BaSO4 content varies from 0 to 1.5%. The crystallization of hematite decreases and the holes whose distribution is uneven increases when BaSO4 content is more than 1.5%. In reduction process, the wustite reduces and metallic iron increases with increasing BaSO4 content from 0 to 5.0%.

The present work was carried out to study the evaporation of fluoride from CaF 2 -CaO-Al 2 O 3 -MgO-Li 2 O-(TiO 2 ) slag with different TiO 2 contents. The evaporation ratio is determined by monitoring the weight change of the slag by isothermal thermogravimetric analysis in the temperature range of 1470-1530°C. The results show that the evaporation ratio of fluoride is promoted by increasing temperature and adding TiO 2 content from 0 to 13.28 wt-%. It has a slight effect to enhance the fluoride evaporation ratio when the TiO 2 content exceeds 8.67 wt-%. CaF 2 and AlF 3 are major constituents of the evaporation substances. The evaporation of fluoride is affected by the vapour pressure of AlF 3 and the viscosity of slag. The evaporation process for TiO 2 -containing slags is controlled by a chemical reaction in the beginning, followed by a mixed reaction-mass transfer regime, and the limiting factor is the liquid-phase mass transport in the end.

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The effect of CaF 2 substitution with TiO 2 on the crystallization characteristics of low-fluoride slag was studied using differential scanning calorimetry (DSC) combined with XRD and SEM-EDS analysis. The effective activation energy for crystallization of the slag was evaluated. The results showed that the liquidus temperature of the slag increased unnoticeably with increasing TiO 2 content. Increasing TiO 2 addition from 4.3 wt% to 13.0 wt% decreased the undercooling of the slag and enhanced the crystallization ability of the slag. There is no change in the types and precipitation sequence of the crystalline phase in the slag with different TiO 2 contents during continuous cooling. The crystalline phases were Ca 12 Al 14 O 32 F 2 , CaTiO 3 , MgO, and CaF 2. The first and second crystallization phase were Ca 12 Al 14 O 32 F 2 and CaTiO 3 , respectively. The dominant crystalline phase was faceted Ca 12 Al 14 O 32 F 2 crystals. The morphology of CaTiO 3 crystal changed from needle-like to blocky with increasing TiO 2 content. The MgO crystal was with little blocky morphology, and the needlelike CaF 2 distributed among CaTiO 3 crystal. The precipitated amount of both MgO and CaF 2 was very small. The effective activation energy for Ca 12 Al 14 O 32 F 2 formation decreased with increasing TiO 2 content in the slag, indicating that TiO 2 enhanced the crystallization tendency of the slag.

This study presents the evaporation mechanism of fluoride from CaF2–CaO–Al2O3–MgO–Li2O–(TiO2) slag and their melting characteristics at different TiO2 contents by thermogravimetric analysis and melting‐temperature‐characteristic testing. FactSage is used to identify the major components evaporating from the tested slags. The results show that the slag melting point decreases with an increase in the TiO2 content. In addition, X‐ray diffraction analysis reveal that with an increase in the TiO2 content, the total CaF2 and Ca12Al14F2O32 content increase while the MgAl2O4 content decrease. The gaseous species easily evaporating from slags, including LiF and CaF2, are the primary contributors to fluoride loss. The apparent activation energy for LiF evaporation is calculated to be in the range of 116.75–227.62 kJ mol−1 and this process can be described as 3D diffusion. In the case of CaF2 evaporation, the apparent activation energy is calculated to be in the range of 365.98–492.33 kJ mol−1 and this process followed the mechanism of random nucleation and growth.